Chemical reactions which take place in the interface of an electric conductor (called an electrode, which can be a metal or a semiconductor) and an ion conductor (the electrolyte) being able to be a solution and in some special cases, a solid, are known as an electrochemical process.
An electrochemical process converts electric energy into chemical energy and vice versa. The non-spontaneous chemical reaction of separating chemical compounds by applying a direct current is known as electrolysis.
If a chemical reaction occurs by means of an externally applied potential difference, it refers to an electrochemical cell. In contrast, if the electric potential drop is created as a result of the chemical reaction, it is known as an “electric energy accumulator”, also called a battery or galvanic cell.
Since the discovery of water electrolysis, the dissociation of the water molecule by means of supplying electricity for producing hydrogen and oxygen, the process has evolved and diversified into the technical industrial solutions known today.
At a very simplified level, the water electrolysis reaction is described by the following reaction:2H2O (l)+electricity→2H2 (g)+O2 (g)
As observed, this chemical reaction is characterized in that the reaction products which are hydrogen (gas) and oxygen (gas) are generated in the stoichiometric ratio of 2:1, which implies that the production of both gases is not the same and neither is the associated fluid dynamics.
With regards to large electrolysis plants, the dominant technology is alkaline electrolysis technology, such as those described in the documents EP 1133586 B1, EP 1464730 A1 and US 200083614A1 which described the representative examples of the state of the art. All of them describe particular electrochemical reactor solutions, also known as stacks. A stack is formed by stacking electrochemical half-cells, such that two electrochemical half-cells result in an electrochemical cell the architecture of which is significant for the system efficiency.
The architecture of an electrochemical half-cell must be understood as its geometry (design) and manufacturing materials, which determines the fluid dynamic and electrochemical behavior and, hence, the efficiency of the operating equipment. The architecture also relates to the basic operation functionality, leak-tightness, mechanical strength under pressure, chemical compatibility with the products used for the reaction and with the products generated therefrom.
The state of the art of the architecture of electrochemical reactors, more specifically of the electrolysis cells, is characterized by the following:
The reactors have half-cells similar in design (geometry and material) both for the anode and the cathode, such as those described in documents EP 1 133586 B1, EP 1 464730 A1 and US 20080083614A1.
The leak-tightness is assured by means of gaskets and/or mechanized tongue and grooves on the surface of the cells. The use of gaskets requires more constructive elements; making the assembly more complex, randomized and unsafe. When the leak-tightness is achieved by means of gaskets or mechanized tongue and grooves, the voltage measurement can only be made between accessible conductive elements; i.e., the end plates of the stacks. Therefore, the voltage measurement can only be obtained for the complete electrochemical reactor as to not compromise the leak-tightness between the electrochemical cells.
As observed, one of the problems of the state-of-the-art electrochemical cells is that gaskets must be used to assure leak-tightness. Another drawback of current electrochemical cells is that due to their mechanical design, the material of the closure element must be such that it supports the pressure of the reactor formed with the cells. Furthermore, up until now, the stoichiometry of the products generated has not been taken into account, i.e., it does not have a half-cell geometry which allows handling them optimally.